This has got to be one of the most useful programs ever.
I use OneNote to keep track of nearly everything, including tax info. (I back it up so it's in 3 places) You can also export sections into PDF etc.
I keep an ongoing record of invoices paid and due, asset register, etc. etc. on pages dedicated to each category in a OneNote notebook labelled by tax year.
Did you know if you select a list (invoice names and numbers with amounts paid, say) in OneNote you can automatically make an excel spreadsheet out of it with one button click and it saves right there on the same page? Another button click opens the spreadsheet for editing in excel. Saves heaps of effort.
Great little program. :)